Clinical trial daily epigallocatechin 3-0 gallate (EGCG) dosage is 9 mg per kilogram of body weight¹ per day, where the EGCG content of Greenselect® is 13%.
Green tea extract has a relatively short half life² (3.4 ± 0.3 h): dosage twice a day.

 
 
ECGC dosage: mg/day
Source   Swanson     Vitacost  
Capsules/Bottle  60 90
Capsule (mg) 600 300
Capsules/Day
Cost/Day
Supply (Days)

Sources

Swanson Ultra
GreenSelect® Green Tea Phytosome – 60 caps, 600 mg: US$28.95 plus shipping
Vitacost
GreenSelect® Green Tea Extract Phytosome – 90 caps, 300 mg: US$13.99 plus shipping
¹ De la Torre R, De Sola S, Pons M, Duchon A, de Lagran MM, Farré M, Fitó M, Benejam B, Langohr K, Rodriguez J, Pujadas M, Bizot JC, Cuenca A, Janel N, Catuara S, Covas MI, Blehaut H, Herault Y, Delabar JM, Dierssen M. Epigallocatechin-3-gallate, a DYRK1A inhibitor, rescues cognitive deficits in Down syndrome mouse models and in humans. Mol Nutr Food Res 58(2): 278-88 (2014 Sep) Revised: July 25, 2015.
² Lee MJ, Maliakal P, Chen L, Meng X, Bondoc FY, Prabhu S, Lambert G, Mohr S, Yang CS. Pharmacokinetics of tea catechins after ingestion of green tea and (-)-epigallocatechin-3-gallate by humans: formation of different metabolites and individual variability. Cancer Epidemiol Biomark Prev 2002;11:1025–1032.